Conventionally, a tire-pressure monitoring device which informs a driver of a tire-pressure information has been known. A tire-pressure monitoring device comprises tire-pressure sensor units (referred to as wheel sensors) for detecting a tire pressure for respective wheels, and is configured to transmit a tire-pressure information as a radio signal from this wheel sensor and receive this radio signal by a vehicle body side device to acquire the tire-pressure information. When judged that the tire pressure has been reduced based on the received tire-pressure information, the vehicle body side device displays that on an annunciator to notify it to a driver.
In such a tire-pressure monitoring device, in order to distinguish from which wheel sensor the radio signal received by the vehicle body side device is transmitted, the radio signal contains a sensor ID which is an identification information of a wheel sensor, in addition to the tire-pressure information. The sensor ID is beforehand registered in the vehicle body side device in association with the wheel location where the wheel sensor is disposed. Therefore, the tire-pressure information can be distinctively acquired for every wheel.
However, when a tire rotation is performed or a wheel is replaced with another one, a registered relation between the sensor IDs and the wheel locations becomes wrong. For such an issue, a device proposed in the Patent Document 1 (PTL1) is configured to automatically distinguish the wheel locations of every wheel sensors. This device comprises an acceleration sensor built in a wheel sensor, detects the turning position of the acceleration sensor based on the gravitational acceleration component of the acceleration in a centrifugal force direction of a wheel detected by this acceleration sensor, and transmits a radio signal containing a tire pressure and a sensor ID at a timing when the turning position of the acceleration sensor is the uppermost.
On the other hand, a vehicle body side device is configured to detect the rotation locations of the respective wheels based on the count values of pulse signals (referred to as wheel-speed pulses) outputted by the wheel-speed sensors, and samples the rotation location data (count values of pulse signals) of the respective wheels whenever it receives the radio signal from the wheel sensor. The wheel sensors rotate integrally with the wheels to which they are attached. For this reason, whenever the wheel sensor and the wheel-speed sensor are disposed corresponding to a common wheel (identical wheel), the wheel rotation location at a transmission timing of the wheel sensor will be always a constant location fundamentally. Using this, the vehicle body side device calculates the variation degree of each rotation location data for every sensor ID, and determines, as a wheel to which the wheel sensor is attached, the wheel with little variation in the rotation location at the transmission timing. Hereafter, the treatment for specifying the wheel to which each wheel-speed sensor is attached will be referred to as a wheel location discrimination treatment.
When a vehicle stops in the middle of the wheel location discrimination treatment, a wheel-speed pulse may be counted up by disturbance such as an oscillation even though the wheel is not rotating. For such an issue, the device proposed in the Patent Document 1 (PTL1) is configured to judge whether the vehicle is stopping and to carry out a subtractive correction of the count values of the wheel-speed pulses counted during its stopping period.